They don't always have to fit the month. Especially considering the fact that northern and southern hemispheres have different experiences throughout the year (yep, believe it or not - for half the globe, January is hot ) But a "theme" is good. All calendars have a theme, that way it ensures those interested in one pic would likely like the rest Whose gonna buy a calendar where one month is a drawing of a dog and the next is a photo of a building etc